Great Tits Use Syntax to Chirp Complex Messages

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Songbirds known as Japanese great tits have figured out how to combine tweets with distinct meanings into more complex sentences, new research finds.

The discovery is a breakthrough in understanding animal vocalizations. Before, it was difficult to prove that any animal created its own complex, structured language, but Japanese great tits appear to have done just that.

“We now have good evidence that animal communication systems share many of the basic properties of human language,” said Toshitaka Suzuki, lead author of the study appearing in Nature. “For example, mammals and birds can use specific call types to denote specific objects, and Japanese great tits can combine different ‘words’ to send a compound message.”

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Suzuki is a postdoctoral fellow in the Department of Evolutionary Studies at Japan’s Graduate University for Advanced Studies. Previously, he determined that Japanese great tits created distinct alarm calls to refer to two of their main nest predators: jungle crows and Japanese rat snakes.

For the new study, he and colleagues David Wheatcroft and Michael Griesser focused on a few of the Japanese great tit’s different note types, which are named A, B, C and D. Prior research found that when A,B, and C are produced together in that order, the call instructs listeners to “scan for danger.” The “D” note instructs listeners to “approach the caller.”

When the birds tweet ABC-D together and in that order, there is a compound meaning that essentially translates to: scan for danger and come here. Suzuki and his team played the recorded calls to 21 adult Japanese great tits in the wild and the listening birds did exactly as the calls commanded, with the birds scanning the horizon and approaching the loudspeaker. When the researchers reversed the order of the notes to D-ABC, the listeners did not respond.

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The study reveals that the birds are capable of a skill known as compositional syntax — meaning they combine distinct elements of their vocalizations and extract a compound meaning from them. Before, only humans were thought to have this ability.

The talent could be common among many different songbird species.

“There is no evidence showing that non-human primates, even chimpanzees, use compositional syntax,” Suzuki said, adding that “combinations of sounds are very common in tits and chickadees, and are also found in other species of passerines (perching birds).”

The birds seem to learn their various calls over time, with nestlings only emitting a limited number of call types associated with begging and distress. As they grow up, they copy their fathers’ mating songs and may learn their vocalizations in other ways, too.

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Save for a handful of talented “polyphonic overtone” singers who can sing two notes at the same time, people are usually limited to producing one sound at a time with their vocal cords. Birds, on the other hand, “can control the two sides of their syrinx independently, allowing them to produce two different sounds simultaneously,” Suzuki said.

It is known that Japanese great tits have AC, BC, AC-D and BC-D calls, as well as probably many others, all of which are not yet understood by researchers.

Robert Magrath, a professor of behavioral ecology at the Australian National University, says the research “is interesting in showing that the specific order of notes in a call can change its meaning for listeners.”

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Magrath added, “This enlarges the opportunities of complex communication from a limited repertoire of call types, and illustrates one way in which there is a similarity between human communication and that of other species.”

In the future, Suzuki and his colleagues hope to learn how Japanese great tits and related species evolved such a sophisticated communication system. They also hope to better determine what is unique about human verbal skills.

It could be that we are the only species that can communicate about the future and the past — this is something that has never been detected in animal communications.

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